(1)∵ In the recorded results,+10 is the largest and -8 is the smallest.

∴90+ 10= 100 (minutes), 90-8=82 (minutes),

∴ The highest score is 100 and the lowest score is 82;

(2)∵

7+(? 1)+9+2+(? 1)+5+(? 8)+ 10+4+9

10

=2.2,

Their average score =90+2.2=92.2 (points),

So their average score is 92.2.